M4.8 Earthquake 193 km WSW of Adak, Alaska — October 4, 2020
2020-10-04 07:11:44 UTC (2020-10-04) · approx. 7:11 PM UTC-12 local
Aftershock of the M5.3 mainshock.
On October 4, 2020 at 07:11 UTC, a magnitude 4.8 shallow crustal earthquake struck 193 km WSW of Adak, Alaska, at a depth of 40.2 km and coordinates 51.2413°, -179.2378°.
Physical scale: An earthquake of magnitude 4.8 releases seismic energy equivalent to roughly 239 metric tons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 1.2 km — a useful intuition for the size of the slip patch on the fault.
This earthquake is part of an ongoing aftershock sequence following the magnitude 5.3 mainshock that occurred 26 days ago 151 km WSW of Adak, Alaska. Since the mainshock, the USGS has recorded 26 aftershocks in this area. Aftershock activity is expected to continue for days to weeks as stresses on surrounding faults redistribute.
The epicenter is located in Alaska, a region characterized by Pacific Plate subduction beneath the North American Plate, producing frequent megathrust and crustal earthquakes along the Aleutian arc. The nearest mapped fault system is the Aleutian megathrust. View all earthquakes in Alaska.
Learn more: Magnitude scale · Aftershock sequences
Earthquake Details
-179.2378°E
Technical Information
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Common Questions
How strong was the magnitude 4.8 earthquake near Adak, Alaska?
The magnitude 4.8 earthquake that struck 193 km WSW of Adak, Alaska on October 4, 2020 at 07:11 UTC had a depth of 40.2 km. For context, this was a light earthquake commonly felt near the epicenter.
Where did the earthquake occur?
The earthquake epicenter was located at 51.2413°, -179.2378°, which is 193 km WSW of Adak, Alaska. View all earthquakes in Alaska.
Were there aftershocks?
Aftershock activity is monitored continuously by the USGS. Aftershock sequences from magnitude 4.8 earthquakes can continue for several days and gradually diminish over time.
Is this the same earthquake as the M5.3 one earlier?
No. This magnitude 4.8 earthquake is an aftershock of the larger magnitude 5.3 mainshock that occurred earlier 151 km WSW of Adak, Alaska. Aftershocks are smaller earthquakes triggered by stress changes from the mainshock.
Has Alaska had earthquakes this big before?
The largest recorded earthquake in Alaska was the M9.2 Great Alaska earthquake of March 27, 1964. Today's magnitude 4.8 event is significantly smaller than that historical record.
Authoritative source: USGS event page (event ID: us6000c5e0). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2020, October 4, 2020). M4.8 Earthquake 193 km WSW of Adak, Alaska — October 4, 2020. Retrieved December 12, 2020 from https://www.earthquaketracker.org/earthquakes/event/us6000c5e0/